1. Field of the Invention
The invention relates to an apparatus for die casting, the use of such an apparatus and a method for die casting.
Die casting is nowadays a widespread and successfully used industrial production process for the primary shaping of parts and products in large numbers. The main feature of this process is that a metal melt in die casting machines is pressed under high pressure at a high speed into a multi-part, usually two-part permanent mould, which is also referred to as a casting tool or moulding tool, from which the die cast part is ejected after having solidified.
The machines for performing the die casting process are usually fully automated nowadays and enable very efficient production of dimensionally accurate die cast parts with high demands on a smooth, clean surface. Die casting machines basically have the task of accommodating the permanent mould, closing, filling and opening the latter and ejecting the die cast part. In the employed permanent moulds, which on account of the occurring mechanical and thermal loads are usually made from heat-resisting materials, preferably from high-strength hot-work steels, metals can be processed at a sufficiently low melting temperature, in particular the metals copper, aluminium, magnesium, zinc, tin, lead and similar metals as well as alloys of these metals.
In connection with this invention, die casting is understood to mean all processes in which at least fluid, pulpy or pasty casting metal is poured into a permanent mould under raised pressure. This includes die casting, squeeze casting, thixocasting, thixomoulding or comparable processes.
The cavity of the permanent mould reproduces the three-dimensional geometry of the die cast part to be cast. The permanent mould is designed so that the solidified die cast part can be removed from the permanent mould without difficulty. For this reason, the permanent mould usually comprises a fixed mould half and a mobile mould half. The two mould halves of the permanent mould are closed in the state ready for casting, i.e. in the casting position. They are kept closed by the closing force or locking force of the die casting machine during the casting process.
When the mould halves are parted, the parting plane is usually positioned in such a way that, during the opening of the permanent mould, the die cast part remains in the mobile mould half and in the opening position can be ejected from the permanent mould.
The two mould halves thus usually define the main mould parting line and usually also form the greater part of the contour of the die cast part to be cast.
Often, however, it is necessary to incorporate so-called fixed cores into the mould halves, said cores chiefly serving to form holes, blind holes, openings or recesses in the die cast part. They must under no circumstances hinder the opening of the permanent mould or the ejection of the die cast part.
Mobile cores and/or contour parts are required for the formation of cavities in the die cast part, for example holes, recesses, openings or blind holes which do not run in the mould-closing direction. Said mobile cores and/or contour parts are designed such that they form the corresponding contour in the die cast part.
These cores are introduced into the permanent mould before the casting and are released again after the casting, i.e. pulled out of the die cast part. Hydraulically or mechanically operated core-pull devices, which are also referred to as core pullers, are normally used for this purpose.
Since mobile cores are shape-forming parts of the permanent mould and come into contact with the liquid metal, they are usually also produced from heat-resisting material.
The mobile cores are usually locked by the two mould halves in an inserted casting position. If locking by means of the mould halves is not possible for design reasons, however, it is necessary when using a hydraulic core-pulling cylinder for the piston force of the latter to be greater than the core explosive force exerted by the casting pressure on the projection area of the core.
When use is made of a hydraulic core-pulling cylinder, the latter is usually also dimensioned in such a way that its tractive force is greater than the shrinkage of the die cast part around the mobile core.
2. The Prior Art
Die cast parts with curved or bent or arc-shaped cavities, i.e. for example with curved channels, openings, holes, recesses or blind holes, cannot be completely produced by means of mobile cores according to the prior art.
For the production of a die cast part, DE 41 02 358 C2 proposes inserting a hollow body filled with a core medium and with a predetermined curvature into the permanent mould. After the die casting, the core medium is removed. The curved hollow body remains in the die cast part and thus forms the desired curved functional cavity. The process is expensive.
Proceeding from the prior art, the problem underlying the invention is to find an alternative solution for producing a die, cast part with an arc-shaped or curved inside and/or outside casting contour.
According to the invention, this problem is solved by an apparatus for producing a die cast part with an arc-shaped or curved or arched outside and/or inside casting contour according to the features of claim 1. Developments and advantageous embodiments emerge from the sub-claims.
The apparatus according to the invention for producing a die cast part with an arc-shaped, curved or arched inside and/or outside casting contour comprises a permanent mould with at least one mobile arc-shaped slide-valve core, which forms the inside and/or outside casting contour of the die cast part, wherein a rotary slide-valve arrangement is provided which moves the slide-valve core before the die casting on an arc-shaped path into the permanent mould and after die casting onto an arc-shaped path out of the permanent mould.
It is thus possible for the first time to produce, with a completely accurate contour, a die cast part with an arc-shaped or curved or arched inside and/or outside contour.
The slide-valve core is moved here about an imaginary centre-point on the arc-shaped path.
A development of the invention makes provision such that the rotary slide-valve arrangement is a mechanical, pneumatic or preferably a hydraulically operated core push-and-pull device.
Furthermore, provision is made such that the rotary slide-valve arrangement comprises an arc-shaped rotary slide valve, preferably in the manner of an annular or flat-ring segment, wherein the rotary slide valve is connected to the slide-valve core at the end face and preferably in a firmly bonded manner.
An advantageous embodiment of the invention makes provision such that the rotary slide-valve arrangement comprises one or more, preferably different, means which is or are in an active connection with the rotary slide valve, in such a way that said means imparts or impart preferably a likewise arc-shaped displacement movement and preferably position-fixing to the rotary slide valve and thus to the slide-valve core.
Provision is expediently made such that the means comprise one or preferably two hydraulic cylinders with a piston rod, wherein the piston rod is in an active connection with the rotary slide valve, in such a way that, when a rectilinear displacement of the piston rod takes place, an arc-shaped displacement movement is imparted to the rotary slide valve and thus on the slide-valve core.
It is advantageous here that the rotary slide-valve arrangement according to the invention does not require a central bearing in order to guide the rotary slide valve on an arc-shaped path. The space for such a central bearing is not available for the production of die cast parts in most cases of application, since this space is required for shape-forming parts, for example of a moulding half of the permanent mould.
Provision is advantageously made such that the rotary slide-valve arrangement comprises a preferably stationary rotary slide-valve guide, which is constituted in such a way that the rotary slide valve, when the latter is pushed or pulled at the end face not connected to the slide-valve core, is moved in an arc-shaped manner in the slide-valve guide.
A further development of the invention makes provision such that the slide-valve guide is constituted as an arc-shaped bush with a cross-section matched to the rotary slide valve, in which bush the arc-shaped rotary slide valve can move.
The hydraulic cylinder with the piston rod is expediently disposed in such a way that, when the rotary slide valve is displaced in the direction of the permanent mould, force is essentially exerted only on the inner face of the arc-shaped rotary slide-valve guide that forms the outer radius and such that, when the rotary slide valve is displaced in the direction of the mould-removal position, i.e. when the rotary slide valve is pulled out, force is essentially exerted only on the inner face of the arc-shaped rotary slide-valve guide that forms the inner radius.
The expenditure of force for the displacement of the rotary slide valve together with the slide-valve core inside the rotary slide-valve guide is thus relatively small and distributes itself, so that the susceptibility to wear can be kept extremely low and the useful life of the rotary slide-valve arrangement is increased.
Furthermore, provision is made such that means are provided for introducing and distributing lubricant, in particular oil or grease, between the rotary slide-valve guide and the rotary slide valve.
According to an advantageous embodiment of the invention, the means comprise at least one distributor groove, which is preferably drawn over the length of the outer radius of the rotary slide-valve guide present on the inner face and is countersunk therein, wherein the distributor groove is connected to at least one supply channel which leads into the rotary slide-valve guide.
Tightness of the rotary slide valve or seizing-up of the rotary slide valve in the rotary slide-valve guide is thus prevented and the durability of these parts is increased.
A further development of the invention makes provision such that the means comprise lubricating grooves which are disposed on the rotary slide valve, wherein the lubricating grooves preferably run in a radiating manner towards the imaginary centre-point of the arc-shaped rotary slide valve. Tightness of the rotary slide valve or seizing-up of the rotary slide valve in the rotary slide-valve guide is thus also prevented and the durability of these parts is increased.
The rotary slide-valve arrangement expediently comprises means which locks or lock the rotary slide valve and therefore the slide-valve core after the movement into the open or closed permanent mould and before the movement out of the open or closed permanent mould and preferably simultaneously apply the main mould-removal force.
A combination slide valve is preferably provided, which is constituted in such a way that, on the one hand, it locks the rotary slide valve together with the slide-valve core after the movement into the permanent mould and moves the rotary slide valve together with the slide-valve core into the final casting position, and that, on the other hand, it unlocks the rotary slide valve together with the slide-valve core before the movement out of the permanent mould, thereby releases the slide-valve core from the die cast part and moves the rotary slide valve together with the slide-valve core into a preliminary mould-removal position.
The combination slide valve makes it possible to dimension the hydraulic cylinder of the rotary slide-valve arrangement relatively small, since the hydraulic cylinder of the rotary slide-valve arrangement is required only for the relatively small force-expending displacement of the rotary slide valve out of the initial position into a preliminary final casting position and out of the preliminary mould-removal position into a mould-removal position, which at the same time is again the initial position. The hydraulic cylinder of the rotary slide-valve arrangement does not therefore have to be constituted in such a way that its piston force is greater than the so-called core explosive force exerted by the casting pressure on the projection area of the slide-valve core. The hydraulic cylinder of the rotary slide-valve arrangement likewise does not have to be constituted so large that the tractive force acting on the rotary slide valve and therefore on the slide-valve core is greater than the shrinkage force of the die cast part around the mobile arc-shaped core.
The combination slide valve can advantageously be operated mechanically, pneumatically or preferably hydraulically, wherein a hydraulic cylinder is preferably provided, the piston rod whereof is in an active connection with the combination slide valve.
The rotary slide valve and the rotary slide-valve guide preferably each comprise a recess, which are constituted in such a way that, after the slide-valve core has been moved into the permanent mould, they form a common opening for accommodating the combination slide valve, wherein the combination slide valve and the opening are constituted in such a way that the rotary slide valve together with the slide-valve core is locked when the combination slide valve is pushed into this opening, wherein the rotary slide valve together with the slide-valve core is moved into the final casting position, and that the rotary slide valve together with the slide-valve core is unlocked when the combination slide valve is pulled out of this opening, wherein the slide-valve core is released from the die cast part and the rotary slide valve together with the slide-valve core is moved into a preliminary mould-removal position.
A development of the invention makes provision such that the combination slide valve and the recess of the rotary slide valve comprise inclined planes, in such a way that, when the combination slide valve is pushed into the recess of the rotary slide valve, the rotary slide valve is displaced in the direction of the permanent mould and such that, when the combination slide valve is pulled out of the recess of the rotary slide valve, the rotary slide valve is displaced in the opposite direction to the permanent mould, i.e. in the mould-removal direction.
It has been shown that it is thus possible, with relatively little expenditure of force, to exert a force on the rotary slide valve that is greater than the core explosive force exerted by the casting pressure on the projection area of the slide-valve core and that the combination slide valve can be moved out of the opening likewise with relatively little expenditure of force, wherein the tractive force acting here on the rotary slide valve and therefore on the slide-valve core is greater than the shrinkage force of the die cast part around the mobile arc-shaped core.
The combination slide valve and the opening are advantageously constituted with a precise fit with respect to one another. The contact faces seal the recess of the rotary slide-valve guide in the final casting position.
An advantageous embodiment of the invention makes provision such that the end face of the slide-valve core not connected to the rotary slide valve is connected after the locking, preferably by contact pressure, to a shape-forming part of the permanent mould, in such a way that the connection is tight with respect to a casting material flowing under pressure.
Furthermore, provision is made such that the casting material is a casting metal and preferably comprises aluminium, magnesium, zinc or alloys with one or more of these metals.
Furthermore, provision is made such that the rotary slide valve comprises edges running conically towards one another at its end face pointing towards the permanent mould, and the permanent mould, which comprises a corresponding recess for the rotary slide valve, comprises contact faces correspondingly running towards one another. Such an embodiment protects against damage to the tool as a result of fretting corrosion. Back-casting of the surfaces due to the molten casting material is prevented. So-called tinsel formation is also reduced.
Tinsel is understood here to mean generally solidified casting metal, usually in the form of thin burrs.
Means are preferably provided which, after the unlocking of the rotary slide valve together with the slide-valve core, blow sealing air into the gap between the rotary slide valve and the permanent mould in the direction of the slide-valve core. This sealing air blows away any tinsel that may be present.
It has been shown that such sealing air also contributes sufficiently to the cooling of the slide-valve core and the rotary slide valve, so that no temperature-regulating channels are required inside the rotary slide valve or the slide-valve core.
The rotary slide valve and the slide-valve core are preferably made from heat-resisting materials, in particular from hot-work steel, the surface of the slide-valve core preferably being nitration-hardened.
Furthermore, the invention relates to the use of an apparatus as described herein for producing die cast parts for the automotive industry, in particular a housing of an internal combustion engine with bent intake manifolds integrally molded in one piece.
Moreover, the invention relates to a method for producing a die cast part with an arc-shaped inside and/or outside casting contour, in particular using an apparatus as described herein, wherein an arc-shaped slide-valve core is moved into a permanent mould before the die casting and out of the permanent mould after the die casting on an arc-shaped path, which is essentially defined by the radius of the slide-valve core.
An advantageous embodiment of the invention makes provision here such that the slide-valve core is moved by means of a rotary slide valve, wherein the rotary slide valve together with the slide-valve core is moved before the die casting by means of a first actuation device into a preliminary final casting position, that a second actuation device then moves and thereby locks the rotary slide valve together with the slide-valve core before the die casting into a final casting position, that after the die casting said second actuation device moves the rotary slide valve together with the slide-valve core into a preliminary mould-removal position, wherein the slide-valve core is released from the solidified die cast part and the rotary slide valve together with the slide-valve core is unlocked, and that finally the rotary slide valve together with the slide-valve core is moved by means of said first actuation device into a mould-removal position, which at the same time is the initial position.